Let me get one thing out of the way, Batman: The Animated Series was my childhood cartoon. I would get up every saturday and be glued to the toob until I got my dose of Kevin Conroy being a demi-god of awesome.
That out of the way, Batman: Mask of the Phantasm marks the ultimate send off to why this show was so dang good. It's well written, introduces a clever and well made new villain and provides by far the best balance between the Bruce Wayne and Batman characters. This movie is why Kevin Conroy will ALWAYS be the Bruce Wayne/Batman character for me. He's able to separate the two characters with just his voice. Christian Bale doesn't hold a candle to this guy.
I'm not going to do a full out review on this thing (as I plan to do a "Batman special countdown" for my web show as we get closer to a Batman 3 release, but I'll just say that if you're even a slim fan of the Animated show then this is worth looking at.
I was able to find a brand new copy on ebay for $5 (including shipping) which is better than what itunes is asking for, happy hunting!